A CRT pacemaker is a known device, for example, as disclosed in EP1108446A1 and its counterpart U.S. Pat. No. 6,556,866 (both assigned to Sorin CRM S.A.S, previously known as ELA Medical). A CRT pacemaker is an active implantable medical device that provides CRT and applies an interventricular delay (“VVD”) between the respective instants of stimulation of the left and right ventricles. The VVD is adjusted to resynchronize the contractions of both ventricles to optimize the patient's hemodynamic status.
In this regard, a simultaneous stimulation of both ventricles is not always optimal as it does not necessarily lead to a synchronous contraction of both ventricles. This is because, first, the right and left conduction delays in the myocardium are not the same and may depend on multiple factors. Second, the location of the left ventricular lead makes a difference, depending on whether it is an epicardial lead or implanted into the coronary sinus. It is therefore desirable to establish a VVD between the two stimuli, and to adjust this delay to resynchronize the contraction of the ventricles and thus ensure a fine optimization of hemodynamics. The VVD can be zero, positive (the left ventricle is stimulated after the right ventricle) or negative (the right ventricle is stimulated after the left ventricle).
It should be understood that the stimulation of a ventricle (right and/or left) can be achieved using a single stimulation site, or simultaneously a plurality of sites.
The physical locations of the intracardiac electrodes in relation to myocardial tissue to be stimulated are called “pacing sites”. These pacing sites are chosen during implantation, by appropriate positioning of the electrodes after verification of the effectiveness of the selected pacing sites. In some cases, a multisite device will have several electrodes placed in the same cavity, and a change in the pacing site in the cavity is possible simply by an internal switching of the device.
CRT pacemakers typically include a classic “dual chamber” pacing mode in which the device monitors ventricular activity after a spontaneous (detection of a P wave of atrial depolarization) or stimulated (application of an A atrial pacing pulse) atrial event. At the same time, the device starts to count a period called “atrioventricular delay” (AVD) such that if no spontaneous ventricular activity (R wave) is detected at the end of this period, then the device triggers a stimulation of the ventricle (application of a V pulse).
Subsequently herein, the term “pacing configuration” means and designates the combination of characteristics relating to i) “pacing sites” (physical position and/or site selection among several possible sites) and ii) setting the VVD and AVD delays.
EP1736203A1 and its counterpart U.S. Pat. No. 7,664,547 (both assigned to Sorin CRM S.A.S, previously known as ELA Medical) discloses a technique for simply, rapidly, automatically assessing the incidence of the various parameters of the CRT therapy, including the AVD and VVD delays, as well as the selection of the pacing sites, so as to optimize the hemodynamic status of the patient.
The device described in this document uses for this purpose the parameters related to endocardial acceleration (EA) to determine the optimal pacing configuration, either at the time of implantation or subsequently. The endocardial acceleration is for example measured by an accelerometer integrated into an endocardial lead, as described for example in EP 0515319 A1 and its counterpart U.S. Pat. No. 5,304,208 (both assigned to Sorin Biomedica Cardio SpA).
Indeed, several clinical studies have demonstrated that the endocardial acceleration is a parameter that accurately and in real time reflects the phenomena contributing to the mechanical operation of the myocardium, and thus provides comprehensive information on the cardiac mechanics, both in the case of normal operation and in the case of a deficient one.
To automatically optimize the pacing configuration in a test mode periodically triggered by the implant, EP1736203A1 and its counterpart U.S. Pat. No. 7,664,547 propose to change the current pacing configuration and to determine for each tested pacing configuration a performance index derived from one or more parameters related to the peak endocardial acceleration (PEA), reflecting the effectiveness of the chosen pacing configuration. The pacing configuration eventually chosen is the one that maximizes the performance index.
A comparable technique, using a combination of several specific indexes is disclosed in EP2070562A1 and its counterpart US Patent Publication No. 2009/0157134 (both assigned to Sorin CRM S.A.S, previously known as ELA Medical).
All the techniques described in these documents are intended to determine an optimal pacing configuration, that is to say a configuration that at some point in the therapy, improves the patient's hemodynamic parameters, especially to increase the myocardium contractility and improve the filling of the cavities and consequently the cardiac output.
The present invention, unlike these prior known techniques, does not seek to determine an optimal pacing configuration. The invention instead relates to a phenomenon called “cardiac remodeling”, which can be defined as the changes of the heart in response to a disease, and is usually associated with a declining patient condition.
Cardiac remodeling is manifested in the long run by an increase in the size of the left ventricle, with a worsening of the ejection fraction and of the intraventricular pressure regime due to the decrease in contractility and/or too high a blood pressure downstream, and in particular a reduction in cardiac output with serious consequences on the body by progression of heart failure.
By stimulating the ventricles in a controlled manner in at least two points, the CRT therapy optimizes the contraction/relaxation cycle, with a direct benefit by facilitating the work of the heart, but without any regression of the previous changes that occurred because of remodeling. In addition, some patients see no significant response to the CRT stimulation, so that CRT therapy does not benefit them.
To reverse the effects of cardiac remodeling, it has been suggested to employ drug therapy, including treatment with beta blockers, as well as non-drug methods including some surgical techniques for reconstruction of the left ventricle, or the use of certain passive mechanical restraint medical devices or cardiac mechanical assistance devices.